Abstract
Ongoing climate change is likely to result in shifts in successional dynamics in boreal mixedwood stands. Using data from provincial forest inventory databases, we examined the occurrence and abundance of the regeneration of various coniferous species (white spruce, black spruce and balsam fir) along an east-west Canadian gradient in aspen-dominated stands. The interpretation of the results was based on environmental conditions, including climate, natural fire regime and human impacts. We found that conifer regeneration was present in aspen stands along the entire gradient, despite differences in climatic conditions and fire regimes between the west (warmer and drier, with large recurrent fires) and east (more humid with relatively long fire cycles). However, abundance and distribution varied from one conifer species to the next. The abundance of white spruce decreased towards the eastern end of the longitudinal gradient, while balsam fir and black spruce abundance decreased towards the west. Although abundance decreased, balsam fir and black spruce regeneration was still present in western Canada. This study shows that it is difficult to interpret the effects of climate change on conifer recruitment without accounting for the superimposed effects of human activities.
Highlights
Trembling aspen (Populus tremuloides Michx.) is one of the few North American tree species that has a transcontinental distribution and is found over a wide range of site conditions [1]
There was no significant east-west gradient when considering the overall abundance of coniferous regeneration in the aspen forests of Quebec and Ontario (QC and ON) compared to Alberta and British Columbia (AB and BC) (Figure 2a, R2 = 0.1)
Our study shows that coniferous regeneration is present in aspen stands across an east-west transect of Canada, with the exception of stands that are affected by human activities
Summary
Trembling aspen (Populus tremuloides Michx.) is one of the few North American tree species that has a transcontinental distribution and is found over a wide range of site conditions [1]. In the case of aspen, its composition could be maintained as pure- and hardwood-dominated stands or a transition may occur that leads to conifer-dominated stands, depending on the local environmental conditions (climate, disturbance regime and soil). The recurrence of large and severe fires can regularly restart forest succession, favoring the establishment of shade-intolerant species, thereby limiting the establishment and development of late-successional species. These latter species require the presence of residual seed trees preserved in unburnt areas in order to successfully reinvade a burn site [3,5,14,16,17,18]; they generally take longer to recolonize a site following fire [19]
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